Methods of and apparatus for forming an article having a tubular portion

ABSTRACT

Method of and apparatus for forming articles, and in particular, for forming articles from billets of solid plastic material wherein a billet to be deformed is positioned within and confined by a die having a variable shape die cavity, pressure is exerted upon the billet to increase the ductility of the solid plastic material thereof by an amount sufficient to allow deformation of the billet to form the article without fracture of the solid plastic material, and varying the shape of the variable shape die cavity in such a manner as to form the article while maintaining the solid plastic material in a state of increased ductility during deformation.

United States Patent [72] Inventors John Wesley Archer Trenton County; Francis Joseph Fuchs, Jr., Princeton Junction, both of NJ. [21] App]. No. 802,040 [22] Filed Feb. 25, 1969 [45] Patented .Ian. 4, I972 [73] Assignee Western Electric-Company, Incorporated New York, NY.

I 54] METHODS OF AND APPARATUS FOR FORMING AN ARTICLE HAVING A TUBULAR PORTION 14 Claims, 8 Drawing Figs.

[52] US. Cl 72/354, 72/377 [51] Int. Cl B2lk2l/02 [50] Field of Search 72/343, 352, 353, 354, 377

[56] References Cited UNITED STATES PATENTS 3,108,502 10/1963 Chatfield 72/354 Primary Examiner-Richard J. Herbst Attorneys-H1 J. Winegar, R. P. Miller and W. M. Kain ABSTRACT: Method of and apparatus for fomiing articles. and in particular, for forming articles from billets of solid plastic material wherein a billet to be deformed is positioned within and confined by a die having a variable shape die cavity, pressure is exerted upon the billet to increase the ductility of the solid plastic material thereof by an amount sufficient to allow deformation of the billet to form the article without fracture of the solid plastic material, and varying the shape of the variable shape die cavity in such a manner as to form the article while maintaining the solid plastic material in a state of increased ductility during deformation.

PATENTED JAN W SHEET 3 [1F 5 FIG. 3

METHODS OF AND APPARATUS FOR FORMING AN ARTICLE HAVING A TUBULAR PORTION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is related broadly to methods of and apparatus for forming articles; and in particular, to methods and apparatus for forming articles having tubular portions, such as cup-shaped articles, from billets of solid plastic material.

The cup-shaped articles which may be formed by the practice of the present invention may be of circular transverse cross-sectional configuration, or otherwise such as of elliptical, polygonal or irregular cross-sectional configuration. The wall thickness of such cup-shaped articles may be uniform or y With regard to the term solid plastic material, it is known by those skilled in the art, that many metals and other materials increase in ductility, or have an increased capacity for deformation without fracture, when they are subjected to high pressure. These metals and other materials are known as solid plastic materials. This principle is treated in P. W. Bridgman, Large Plastic Flow and Fracture, published by McGraw-I-lill Book Company of New York in 1952. Accordingly, it will be understood that the expression solid plastic material as used in this specification and claims, is used in this context. I

However it will be understood that this invention is not limited to practice with such defined solid plastic material, but is equally useful with regard to other materials or compositions which may or may not fall expressly within such materials definition, such as for example, a slurry, comminutized or granulated material, etc.

2. Description of the Prior Art Generally speaking, known methods for manufacturing cupshaped articles include machining processes, extrusion processes and deep drawing processes. The choice of one of these particular processes from among the others is ordinarily determinable from the required dimensions of the article to be formed and the characteristics of the material from which the article is to be manufactured.

Each of the above-noted processes, as practiced in the prior art, has been accompanied by limitations and disadvantages which have restricted its commercial exploitation. More particularly, the deep drawing and extrusion processes, each of which involves the deformation of material from an initial shape to come desired finished configuration, are limited by the ductility of the material to be deformed, in particular, the ductility of the material at atmospheric pressure. Thus, if the formation of an article from a billet of material by a deformation process requires deformation of the material by an amount which would be in excess of its ductility, the use of a deformation process is impossible since, upon being deformed to the limit of its ductility, i.e., its fracture point, the material will fail prior to the completion of formation of the desired article. Machining processes, which do not involve the deformation of material, and which, therefore, have been utilized in situations wherein manufacture by deformation processes has been rendered at least commercially infeasible, are disadvantageous in that they are extremely time consuming and expensive. Thus, those having skill in this art recognize that, if at all possible, machining processes should not be utilized if manufacture can be satisfactorily accomplished by deformation processes.

Considering specific limitations and disadvantages of the above-noted prior art cup-shaping processes as heretofore practiced in the art, it is generally recognized by those skilled in the art that the use of deep drawing processes for forming cup-shaped articles is limited to the manufacture of cupshaped articles the wall thicknesses of which are not less than to 20 percent less than the original thickness of the material being deformed. Specifically, deep drawing processes ordinarily comprise the positioning of a blank of material over a die having an opening, the inside diameter of which opening conforms to the desired outside diameter of the cup-shaped article to be formed, and thereafter advancing a plunger against the blank and into the die opening so as to draw the blank material into the die opening to form the desired cupshaped article. The outside diameter of the plunger corresponds to the desired inside diameter of the cup-shaped article to be fonned and therefore the plunger and die opening cooperate to define the wall thickness of the article being formed. This wall thickness, as noted above, ordinarily has been limited to be no less than 10 to 20 percent thinner than the thickness of the original blank, or, in terms of the structure of the cup-shaped article being formed, the thickness of the cup wall portion can be no more than 10 to 20 percent thinner than the thickness of the base portion. Clearly, sucha limitation restricts the availability of deep drawing as a process for manufacturing cup-shaped articles which desirably have wall portions which are thinner than percent of the thickness of the base portion.

Extrusion processes for fonning cup-shaped articles have been utilized for many years. Ordinarily, such processes are single operation processes which comprise positioning of a bi]- let of material within the opening of a cylindrical die, the inside diameter of which corresponds to the outside diameter of the cup-shaped article being formed. One end of the billet is then supported within the die and the other end of the billet is subjected to a deforming force by a punch which is advanced thereagainst. The outside diameter of the punch corresponds to the inside diameter of the cup-shaped article to be formed. Thus, as the punch is advanced against the billet within the die, the billet material in line with the path of advance of the punch is displaced laterally toward the surface of the die and thereafter longitudinally between the punch and the die to become the wall portion of the article being formed.

In the early apparatus for practicing most extrusion processes for forming cup-shaped articles, the cylindrical die was held stationary and the billet material was caused to flow between the die surface and the surface of the advancing punch in such manner as to generate relative movement between the material undergoing deformation and the surfaces of both the die and the punch. Such relative movement required that the working forces applied to the material in deformation be sufficiently high to overcome the friction generated between the material in deformation and both the plunger surface and the die surface. Thus, the total force applied to the material in deformation was required to be that necessary not only to deform, but to overcome the abovenoted frictional forces. As a result, the stresses attendant to the exertion of such forces on the material were such as to cause the early occurrence of f fracture by reaching the duetility limit or fracture point of the material, as discussed above, thereby severely limiting the amount of deformation that could be undertaken and therewith the configuration of cupshaped article that could be deformed.

An improvement in extrusion processes occurred when extrusion apparatus were proposed wherein the cylindrical dies within which the cup-shaped articles were to be formed were caused to move with the material being deformed during the deformation process in an attempt to eliminate one of the sources of friction, viz the friction between the cylindrical die and the material in deformation. Such processes, an example of which is disclosed in US. Pat. No. 1,702,278, which was granted on Feb. 19, 1929 to A. Simons, although improved, were still extremely limited in their capability to form cupshaped articles in that notwithstanding the substantial elimination of frictional load from the one source, their practice still required the exertion of great force against the material to accomplish the necessary deformations. The net result of such large forces was exactly that which had been experienced previously, the occurrence of material stresses which quickly reached the fracture points of the materials. Thus, the ductility of the material being deformed continued to limit the utility of the extrusion processes as a method for manufacturing cupshaped articles.

Machining processes for manufacturing cup-shaped articles have been resorted to in those manufacturing situations wherein drawing is not appropriate and wherein the use of extrusion processes for the formation of tubular or cup-shaped articles is because the amount of deformation required would cause the fracture point of the material to be exceeded prior to the completion of the forming process. As is known by those skilled in the art, machining processes are extremely complex and therefore expensive. For example, a typical machining process for manufacturing a cup-shaped article from bar stock ordinarily includes the steps of drilling the stock to form a rough cup cavity, turning the outside diameter of the workpiece to exact dimension, boring the rough cup cavity to form a finished cup cavity, cutting the workpiece to appropriate length, deburring, and cleaning the machined article. Thus, the desirability of being able to form cup-shaped articles by single operation deformation processes which heretofore have only been capable of manufacture by machining is self-evident. Accordingly, it is to overcoming this problem, i.e. the necessity for manufacturing tubular and cup-shaped articles by machining, that the invention is primarily directed.

SUMMARY The present invention overcomes the disadvantages noted above with respect to the prior art processes by providing a method and apparatus for forming articles, which method and apparatus are not limited by the ductility of the material, i.e. the ductility under atmospheric conditions. Specifically, by not being so limited, the method and apparatus of the present invention enable the formation of articles having tubular portions, such as cup-shaped articles, from billet material by a single manufacturing process, which articles heretofore have been capable of manufacture only by machining processes. The process of he present invention may include the steps of confining a quantity of material in a die system including an outer die, a punch, and a mandrel which together define an enclosed die cavity; moving dies of said die system to pressurize said material and moving said outer die and mandrel relatively, while maintaining said die cavity constant in volume and the blank pressurized, to produce said article.

Apparatus in accordance with the present invention may include die means for defining an enclosed variable shape die cavity; and means engaging said die means for (i) varying the shape of said die cavity to initially confine and pressurize a quantity of material and, thereafter (ii) varying the shape of said die cavity while maintaining the volume thereof constant to deform said material to form said article while maintaining said material confined and pressurized.

BRIEF DESCRIPT ION OF THE DRAWING A more complete understanding of the present invention may be had from a consideration of the following detailed description when read in the light of the attached drawings wherein:

FIGS. 1A, B and C are cross-sectional elevational views of a basic apparatus according to the present invention, the views showing the apparatus during progressive steps of the inventive method;

FIG. 2 is a cross-sectional elevational view of a novel apparatus for practicing the method of the present invention, the apparatus being shown in position for receiving a blank prior to deformation;

FIG. 3 is a view similar to that of FIG. 2 but with the apparatus shown in position for the commencement of blank deformation;

FIG. 4 is a view similar to that of FIG. 2 but with the apparatus shown at the completion of the deformation step; and

FIG. 5 is an exploded, partial cross-sectional perspective view of the segmented die of the apparatus of FIGS. 24.

DETAILED DESCRIPTION The method of the present invention may be more clearly described with reference to FIG. 1 wherein apparatus designated generally by the reference numeral 10, is shown in three stages (FIGS. 1A, 1B and 1C) of the process of the present invention for manufacturing a cup-shaped article.

More specifically, a generally cylindrical outer die section 12 is mounted for controlled, longitudinal reciprocation by suitable means (not shown). Outer die section 12 is provided with a first bore 14 which defines a die bore and extends from the upper surface of outer die section 12 axially through a portion thereof, and a second bore 15 which is coaxial with die bore 14 and extends from the lower surface of outer die section 12 to communicate with die bore 14. The diameter of the die bore 14 corresponds to the desired outside diameter of the cup-shaped article to be formed, and the diameter of the second bore 15 corresponds to the diameter of the opening or cavity to be formed in the cup-shaped article. The intersection of die bore 14 with the second bore 15 defines a radially extending shoulder 16 which is substantially equal in width to the wall thickness of the cup-shaped article to be formed.

The upper end of die bore 14 is closed by a reciprocable ram 17 which is of a diameter substantially equal to and slidably received within thedie bore 14. Rigidly secured to a suitable support means 20, and slidably received within second bore 15 is a mandrel or inner die section 19, the diameter of which, and the conical leading end 21 of which, are shaped to define the desired configuration of the cavity of the cup-shaped member to be formed.

The surface of die bore 14, mandrel 19 and the transverse surface of ram 17 cooperate to define a die cavity 22 for receiving therein a quantity of material such as a billet 23 of solid plastic material, to be deformed. Because the outer die section 12 and ram 17 are both movable with respect to mandrel or inner die section 19, die cavity 22 comprises a die cavity the shape of which is variable.

Referring now to FIG. 1A, the first step of the operation of the apparatus in accordance with the method of the invention comprises positioning a billet 23 within variable shape die cavity 22. Thereafter, ram 17 is advanced (moved downwardly as seen in FIG. 1) within die bore 14 against billet 23 so as to cause deformation of the billet material around the conical leading end 20 of mandrel 19. Thus, ram 17 is advanced from the position shown in FIG. 1A to the position shown in FIG. 18 so as to vary the shape of die cavity 22. Variation of the shape of die cavity 22 in this manner causes the billet material to completely fill or be confined by die cavity 22. In this regard, it is to be understood that the term confine as used in this specification and in the accompanying claims with respect to the containment of billet material within variable shape die cavity 22, connotes not only that the billet material is contained within the die cavity, but also that the billet material is in complete surface-to-surface contact with the die cavity and the volume defined by the die cavity is equal to the volume of billet material contained therein.

For most materials from which cup-shaped articles are ordinarily formed, the amount of deformation experienced in filling the die cavity 22 in the manner shown, i.e. by advancing ram 17 against billet 23, is well within the limits of the ductility at atmospheric pressure or ordinary deformation capability of the materials. There are brittle materials, however, which at atmospheric pressure, have a ductility limit or fracture point which is less than that required even for defonning the billet to fill the die cavity with blank material. In such situations, it may be necessary to preshape the highly brittle billets in such a manner as to enable the die cavity to be filled with billet material without causing deformation in excess of that of which the material is capable. Once the die cavity is filled, however, the confined material can be pressurized so as to increase, if required, its ductility or capability for deformation without fracture.

With the billet 23 confined within variable shape die cavity 22 as shown in FIG. 18 continued pressure is exerted by ram 17 against the confined billet material. The pressure exerted by ram 17 is of sufficient magnitude to increase the ductility of the billet material from that which is ordinarily characteristic of the material at atmospheric pressure, to that ductility which is required to accomplish the necessary deformation for cupshaping without resulting in fracture. When such a state of increased ductility is achieved, the final deformation of the billet 23 can be undertaken.

Referring again to FIG. 1, therefore, it can be seen that in the final step of the forming operation, both the outer die section 12 and ram 17 are advanced concurrently from the position shown in FIG. IE to the position shown in FIG. 1C so as to vary the shape of die cavity 22 from that corresponding to the shape of confined billet 23 to that corresponding to the desired shape of cup-shaped article 26. During the concurrent advancement of cylindrical die 12 and ram 17, die 12 is advanced longitudinally axially through a distance equal to the length of the walls of the cup-shaped article to be formed. Further, the concurrent advance of ram 17 and cylindrical die 12 is coordinated to maintain the volume of die cavity 22 constant, i.e. equal to the volume of the contained billet material, so as to maintain billet 23 confined at all times during deformation, and to maintain the confined billet material, if solid plastic material, in a high-pressure state thereby maintaining the material in a state of increased ductility so as to allow the deformation thereof to occur without fracture.

It is to be recognized that the exertion of pressure on billet 23 to increase the ductility of the solid plastic material thereof and to accomplish the deformation thereof from the billet shape of FIG. 18 to the cup shape of FIG. 1C can be accomplished in more than one manner. More particularly, in apparatus such as that shown in FIG. 1, the surface of die bore 14 is a smooth surface and, as a practical matter in the light of the pressures experienced during deformation, the die bore surface generates little, if any longitudinally directed forces. Thus, the entire force necessary to establish the high pressure required to adequately increase the ductility of the billet material and that force necessary to stress the pressurized billet material to accomplish deformation, must be exerted by ram 17 alone. In apparatus of this type, therefore, outer die section 12 serves solely to enable the controlled variation of the shape of variable shape die cavity 22. In other apparatus, however, the surface die bore 14 may be provided with a textured or otherwise roughened surface, for example the threaded surface of die bore 129 of the apparatus 40 of FIGS. 24. In such apparatus, the high friction surface of the die bore is capable of exerting axially directed forces on the billet material which can assist ram 17 in stressing the billet material during the deformation thereof from billet shape to cup shape. Thus, by providing for the exertion of forces against the billet material by both the ram and the surface of the die bore during deformation, the load on the ram is decreased and a more intimate engagement between the outer die section and the billet material is established, which engagement facilitates a closer control of the shape of the variable shape die cavity.

Upon the completion of the deformation of the billet 23 to form cup-shaped article 26, ram 17 is retracted (moved upwardly as seen in FIG. 1), outer die section 12 is retracted to free article 26 from mandrel l9, cup-shaped article 26 is removed from the apparatus and a new billet 23 is positioned within die 12 in preparation for repeating the process.

The advantages offered by the method and apparatus of the present invention as described above include the substantial elimination of relative movement between the billet material and the surface of die bore 14, and the capability of confining, prepressurizing and maintaining pressurized during deformation of the billet material so as to increase its ductility or capability for deformation without fracture, thereby facilitating the manufacture of cup-shaped articles which heretofore could only be manufactured by machining.

It is to be noted that the basic apparatus disclosed in FIG. 1 includes inner die or mandrel 19 as a fixed element, with outer die section 12 and a ram 17 as movable elements. The purpose of providing two elements of the three part die structure with a capability for movement, is to provide a die having a variable shape die cavity wherein relative movement between the billet material and the surface of one element, viz the die bore of outer die section 12, is substantially eliminated during the deformation of the confined billet, and wherein the volume of the die cavity defined by the elements can be selectively controlled.

The manner in which the relative movement between the billet material and outer die section 12 is substantially eliminated, and the manner in which the volume of die cavity 22 is controlled can be more clearly described with reference to FIGS. 13 and 1C. In FIG. 1B, billet 23 is shown as being confined within variable shape die cavity 22 and pressurized by the action of ram 17 exerting downwardly directed force thereon. In this configuration, the volume defined by die cavity 22 is equal to the volume of billet material 23 contained thereby. Further, as was noted above, in order to maintain billet 23 confined and pressurized during the deformation thereof to form cup-shaped article 26, the volume of die cavity 22 must be maintained constant during the variation of its shape from that conforming to the billet 23 (FIG. 18) to that conforming to the cup-shaped article 26 (FIG. 1C). In order to maintain this constant volume relationship, therefore, the rate of increase of the volume of the wall portion of the cupshaped member must be equal to the rate of decrease of the volume of the base portion of the cup-shaped article being formed. Since the cross-sectional area of the material in the wall portion is less than that in the base portion by an amount equal to the cross-sectional area of mandrel 19, it becomes evident that in order to maintain the desired constant volume relationship between the die cavity and the billet material, outer die section 12 must be advanced at a faster rate than ram 17. Any particular relationship between the two elements is determinable mathematically by anyone of ordinary skill in the art.

In moving from the position shown in FIG. 18 to that shown in FIG. 1C, outer die section 12 moves through a distance d which is equal to the length of the wall portion of the cupshaped article 26. Further, it can be seen that the movement of the billet material during deformation involves a lateral displacement of material above mandrel 19 out of the path of inner die section on mandrel 19 and into the volume of the die cavity which defines the wall portion of the cup-shaped article being formed. Thus, once a unit of billet material is displaced around mandrel 19 from a point in the base portion of the material to a point in the wall portion, it ceases to experience any relative movement with respect to outer die section 12 and advances axially therewith at an equal rate along mandrel 19. Clearly, if such were not the case and a relative movement occurred between the material in the wall portion and the surface of die bore 14, the equality of volumes would be destroyed, the billet material would no longer be confined, and the pressurization of the billet material with its attendant increase in ductility would be lost. The work required to overcome the friction between the billet material and the surface of die bore 14 is substantially eliminated, therefore, because there is no relative movement between material in the wall portion and the die bore as noted above, and because the only relative movement experienced is that between the base portion of the billet material and the die bore adjacent ram 17.

It will also be recognized that the desired relative movement between the outer and inner die sections 12 and 19 respectively and punch 17 as described above, can be accomplished by providing any two or all three of the elements with a capability for movement. Thus, it is not necessary that mandrel 19 be a fixed element; either of the other elements can be fixed so long as the remaining two elements are controllably moveable.

In order to realize fully the advantages which the present invention offers, i.e. in order to facilitate the forming of cupshaped articles by a single deformation operation from materials which would be incapable of single operation deformation without fracture under ordinary ductility conditions, deformation apparatus must be provided which is capable of exerting and supporting the pressures necessary for increasing the capability of billet of solid plastic material to be deformed without fracture. in other words, apparatus must be provided for establishing a high-pressure environment in which to conduct the article forming process. The magnitude of the pressures which may be required can become quite high. For example, in deforming a 98 percent nickel rod billet, 0.151 inch long and 0.180 inch in diameter, into a cup-shaped article which is 0.180 inch in diameter and 0.405 inch long, and which has walls which are 0.392 inch long and 0.010 inch thick, it has been found that prepressurization of the billet material to approximately 250,000 psi. and ultimate pressurization to approximately 450,000 p.s.i. for introducing the necessary stresses for deformation, are sufficient for accomplishing the manufacture of a finished cup-shaped article in a single operation. Clearly, apparatus for generating and supporting such pressures as well as for accomplishing material deformation under such high-pressure environmental conditions, must be sufficiently strong and well supported to accomplish these functions.

FIGS. 2-4 show a novel apparatus, designated generally by the reference numeral 40, in accordance with the present invention, which is capable of generating and supporting pressures of such magnitude as are necessary to increase the duetility and facilitate the deformation without fracture of materials which would otherwise fracture under atmospheric ductility conditions.

Apparatus 40 includes a machine block 42 which is rigidly secured to a foundation member 43 by suitable means (not shown). Machine block 42 is provided with a bore 45 with extends longitudinally into a portion of machine block 42 from the lower surface thereof as seen in FIG. 2. The outer portion of bore 45, the lower portion as seen in FIG. 2, is provided with a threaded counterbore 49 for securely receiving an end plug 50. Counterbore 49 and bore 45 cooperate to define a shoulder 48 which engages the upper surface 51 of end plug 50 to limit the entry of end plug 50 into machine block 42.

As noted above, main bore 45 extends longitudinally into only a portion of machine block 42. Thus, the inner end of bore 45, i.e. the upper end as seen in FIG. 3, defines a transverse surface 52 in which there is formed a longitudinally extending annular channel 54, the purpose of which is discussed below.

Extending longitudinally into machine block 42 from the upper surface 53 thereof, and coaxially with main bore 45, is a bore 55 which communicates with main bore 45 through a mandrel bore 56. Bore 55 accommodates both the base portion 58 of a mandrel 59 which extends into main bore 45 through mandrel bore 56 and a plug 60 which serves as a bearing element between the base portion 58 of mandrel 59 and the surface of foundation member 43.

End plug 50 is provided with a longitudinally extending through-bore 61 which is of smaller diameter than main bore 45 and cooperates therewith to form a stepped cylinder for slidably receiving a stepped piston-vessel 63 therein. As is discussed in detail below, piston-vessel 63 is a piston in the sense that it responds to exerted fluid pressures to reciprocate the outer die section of the apparatus in the manner discussed in detail above with respect to the apparatus of FIG. 1, and is a vessel in that it provides radial support for the pressures generated during the deformation process.

Piston-vessel 63 is a stepped cylindrical member, outer surface of which comprises an upper portion 64, the diameter of which is substantially equal to the diameter of main bore 45, and a lower portion 65, the diameter of which is substantially .equal to the diameter of bore 61 in end plug 50. Connecting the surface of upper portion 64 with the surface of lower portion 65 is a radially extending annular shoulder 66 which cooperates with the upper surface 51 of end plug 50, the surface of main bore 45 and the surface of lower portion 65 of piston-vessel 63 to define an advance fluid chamber 70 (FIG. 4). Extending longitudinally into piston vessel 63 from the lower surface thereof as seen in FIG. 2, is a first bore 67 the upper end of which is provided with threads 68 for rigidly receiving a lower end cap 69. Extending longitudinally into piston vessel 63 from the upper surface 71 thereof, is a threaded second bore 73 for rigidly receiving an upper end cap 75. Disposed between first bore 67 and second bore 73 is a stopped annular shoulder 77, the upper step of which cooperates with upper end cap 75 to define an annular channel 78 and the lower step of which cooperates with lower end cap 69 to define an annular channel 79. As is discussed below, the inner surface of shoulder 77 defines one surface of a support fluid chamber for containing fluid for supporting the pressures experienced during workpiece deformation, and the annular channels 78, 79 accommodate fluid pressure seals 81 and 82 relatively, for preventing the leakage of fluid from the fluid chamber.

Extending longitudinally into lower end cap 69 from the lower surface 84 thereof is a ram bore 86, which communicates with a punch bore 89 extending longitudinally into lower end cap 69 from the upper surface 88 thereof. Ram bore 86 is larger in diameter than punch bore 89 and the inner transversely extending surface connecting the two bores thus defines a shoulder 90, the purpose of which is discussed below.

Upper end cap 75 is provided with a longitudinally extending mandrel bore 92 therethrough and an annular shoulder 94 extending upwardly from the upper surface 95 thereof. Annular shoulder 94 is slidably receivable within the annular channel 54 of machine block 42 and cooperates therewith to divide the space in main bore 45 above piston-vessel 63 into a central chamber 97 and an annular outer chamber 98. Also provided in upper end cap 75 are a plurality of fluid passages 101 for communicating central chamber 97 with the lower surface 102 of upper end cap 75 adjacent mandrel bore 92. The radially outer portion of the lower surface 102 of upper end cap 75 is relieved to define an annular shoulder 104, the purpose of which is discussed below.

The lower surface 102 of upper end cap 75, the upper surface 88 of lower end cap 69 an the surfaces of shoulder 77 and channels 78 and 79 of piston-vessel 63 all cooperate to define a chamber within which is received a die apparatus designated generally by the reference numeral 108.

Die apparatus 108, which as shown in partially cutaway perspective in FIG. 5, comprises a mandrel 59, a punch element 109 and an outer die section designated generally by the reference numeral 110. Punch 109 and outer die section 110 are both axially movable and cooperate with fixed mandrel 59 to define a variable shape die cavity 111. Outer die section 110 is an expandable forming die including a plurality of generally wedge-shaped segments 112 which are positioned for limited radial movement toward and away from the shoulder 77 of piston-vessel 63. The radially inward movement of segments 112 is limited by the surface-to-surface engagement of the radially extending surfaces 114 on each of the segments 112. The radially outward movement of segments 112 is limited by a sealing cylinder 116 which is positioned concentrically of segments 112 when considered collectively. In addition to restricting the outward radial movement of segments 112, sealing cylinder 116 also cooperates with annular shoulder 77 and seals 81 and 82 in annular channels 78 and 79 to define a support fluid chamber 117 (FIG. 2) for containing pressurized fluid to support the radially directed forces which are generated during the deformation process.

Referring to FIG. 5, it can be seen that there are formed on the upper and lower outer peripheral surfaces of segments 112 upper and lower shoulders 1 18, 1 19 respectively, which shoulders define bearing surfaces for upper and lower spring elements 121 and 122, respectively. Spring elements 121 and 122 are normally open elements which constantly urge segments 112 outwardly against the restraining action of sealing cylinder 1 16.

Formed on the radially inner axially extending surface of each wedge-shaped element 112 is an upper arcuate surface 124 and a lower arcuate surface 125. Lower arcuate surface 125 is disposed radially outwardly of upper arcuate surface 124 by an amount substantially equal to the desired wall thickness of a cup-shaped article to be formed. Considering the segments 112 collectively and in their radially inwardly disposed positions as shown in FIG. 5, it can be seen that upper arcuate surfaces 124 cooperate to define a mandrel die bore 127, and lower arcuate surfaces 125 cooperate to define a forming die bore 129. The intersection of mandrel die bore 127 with forming die bore 129 defines a radially extending shoulder 130 which is of a depth substantially equal to the desired wall thickness of a cup-shaped article to be formed. Further, the entire surface of die bore 129 is provided with a shallow spiral thread 131 which renders the surface of die bore 129 a high friction surface of the type discussed above generally with respect to FIG. 1.

Referring again to FIG. 2, punch 109, having a base 137, is secured on the upper surface of a ram 139 by a ring 140 and a retaining plate 141. Punch 135 extends coaxially with punch bore 89 and, as is discussed below, is slidably receivable therein. Surrounding punch 109 is a spring 143 which supports a billet retainer plate 144. Formed centrally of plate 144 is a cylindrical journal 145 adapted for slidably receiving punch 109 therethrough and also for retaining a billet 148 therein during the first phase of the operation of the apparatus.

The operation of the apparatus 40 is effected by the selective introduction of pressurized fluids to the various chambers of the apparatus. The introduction of such fluids is accomplished through suitable passages formed in the apparatus. More specifically,-formed in machine block 42 is an ejection fluid passage 150 which communicates central chamber 97 with a source line 152 of suitably pressurized ejection fluid, a retraction fluid passage 154 which communicates outer chamber 98 with a source line 155 of suitably pressurized retraction fluid, and a vent passage 158 for venting annular bore 54 above annular shoulder 94. Formed in end plug 50 is an advance fluid passage 160 for communicating advance fluid chamber 70 with a source line 161 of suitably pressurized advance fluid. Finally, formed in piston-vessel 63 is a support fluid passage 164 which communicates support fluid chamber 117 with a source line 165 of suitably pressurized support fluid. The required magnitudes of the pressures of the various fluids noted above are dictated by the shape of the article being formed and the material being deformed. By way of example, the pressures required to accomplish the formation of the cup-shaped article from a 98 percent nickel rod billet discussed above were approximately as follows: ejectior. .luid pressurel p.s.i.; retraction fluid pressure 1,100 p.s.i.; advance fluid pressure 1,100 p.s.i.; and support fluid pressure 35,000 p.s.i.

Leakage of pressurized fluids from the respective chambers within apparatus 40 is prevented by the provision of seals mounted in suitable channels formed appropriately in the apparatus elements. More specifically, the leakage of retraction fluid from outer chamber 98 is prevented by a seal 170 mounted in a suitable annular channel formed in annular shoulder 94 for sealing engagement with the surface of channel 54, and a seal 171 mounted in a suitable annular channel formed in the upper portion 64 of the outer surface of pistonvessel 63, for sealing engagement with the surface of main bore 45. The leakage of advance fluid from advance fluid chamber 70 is prevented by seal 171 described above, a seal 174 mounted in a suitable annular channel formed in the lower portion 65 of piston-vessel 63 for sealing engagement with the surface of through-bore 61 in end plug 50, and a seal 176 mounted in an annular channel formed in the upper outer surface of end plate 50, seal 176 being in sealing engagement with the inner surface of counterbore 49 in machine block 42. Finally, as mentioned above, support fluid chamber 117 is sealed against leakage by high-pressure seals 81 and 82 mounted in channels 78 and 79, respectively.

The operation of forming apparatus 40 is best described with reference to FIGS. 2-4 wherein FIG. 2 shows the apparatus in an open or billet receiving position, FIG. 3 shows the apparatus at the commencement of deformation of the billet 148, and FIG. 4 shows the apparatus at the completion of the deforming process.

With particular reference to FIG. 2 showing apparatus 40 in an open position, punch 109 can be seen to be withdrawn from forming die bore 129, punch bore 89 and ram bore 86. With punch 109 withdrawn, spring 143 is fully extended so as to position billet retainer plate partially beyond the end of punch 109. The extension of plate 144 partially beyond the end of punch 109 causes the formation of a billet retainer cup 146 by the cooperation of journal and the upper end surface of punch 109.

Assuming, for purposes of describing the operation of the apparatus in FIGS. 2-4, that the pressures in all operating fluid systems, i.e. the ejection fluid, retraction fluid, advance fluid and support fluid systems, are initially relieved, and that although not pressurized the retraction fluid, advance fluid and support fluid systems are all filled with fluid, the first step of the operation is to position a billet 148 within billet retainer cup 146. The support fluid in support fluid chamber 117 is then pressurized by the introduction of fluid pressure through support fluid source line 165 and passage 164 in piston-vessel 63. The pressurization of the support fluid in chamber 117 generates a radially inwardly directed force against sealing cylinder 116, which in turn bears against the outer surfaces of segments 112 causing them to be displaced radially inwardly against the expanding forces exerted by upper and lower spring elements 121 and 122 as discussed above. The inward displacement of segments 112 continues until the radially extending surfaces 114 are engaged and the upper 124 and lower 125 radial surfaces (FIG. 5) of each segment cooperate to define mandrel die bore 127 and forming die bore 129. The magnitude of the pressure exerted by the support fluid in chamber 117 is such as to close the die segments as described above and to prestress the segmented cylinder formed by the closed segments so that the radially outwardly exerted pressures generated against the surfaces 125 of the segments during deformation are insufficient to open the die.

With expandable outer die section 110 in the closed position, ram 139 is advanced by suitable means (not shown) so as to introduce billet 148 and punch 109 into forming die bore 129 through punch bore 89. During the advance of ram 139, billet 148 is retained in billet retainer cup 146 until plate 144 engages shoulder 90 of ram bore 86 and is held thereagainst by spring 143 during the continued advance of ram 139, punch 109 and therewith billet 148. Once having cleared billet retainer cup 146, billet 148 is retained in position on punch 109 by punch 89 and forming die bore 129 during the advance of billet 148 into abutment with the end of mandrel 59, i.e. to the position shown in FIG. 3.

Considering FIG. 3, billet 148 is shown being retained in position by the lower end of mandrel 59, the upper end of punch 109 and the surface of forming die bore 129. As was discussed above with respect to the description of FIG. 5, there is formed on the surface of die bore 129 a shallow thread 131. The diameter of forming die bore 129 as measured from top to top of the thread 131 is substantially equal to the diameter of billet 148 and also equal to the desired diameter of the finished cup-shaped article. The depth of the threads may be as desired, but it has been found that a thread depth equal to or less than one half of the allowable diameter tolerance of the final article allows a finished article to be formed in one operation without the necessity for further manufacturing steps such as sizing and the like.

With the apparatus positioned as shown in FIG. 3, pressure is introduced to the retraction fluid in outer chamber 98 from source line (FIG. 2) through retraction fluid passage 154. The pressurization of the fluid in outer chamber 98 generates a force against piston-vessel 63 which holds the shoulder 66 of piston-vessel 63 finnly against upper surface 51 of end plug 50 as to facilitate the initial deformation of billet 148 without axial movement in outer die section 110.

With piston-vessel 63 and therewith outer die section 110 so held against axial movement, ram 139 and therewith punch 109 are further advanced against billet 148 so as to cause the billet 148 to be deformed over the conical end blank of mandrel 59 into the root sections of cavity thread 131 so as to completely fill variable shape die cavity 111 as defined by mandrel 59, forming die bore 129 and the upper end of punch 109 with billet material. This step in the operation of the apparatus corresponds to that operation discussed with respect to the apparatus of FIG. 1 in moving from the position shown in FIG. 1A to that shown in FIG. 1B. The material of billet 148, now fully confined within die cavity 111, is pressurized by the exertion of force thereon by punch 109. The magnitude of the pressurization of the material of billet 148 by punch 109 is sufficient to increase the ductility of the billet material sufficiently to facilitate the deformation of the material to form the desired cup-shaped article without the fracture thereof.

Having now fully confined and pressurized the material of the billet within die cavity 111, the pressure of the retraction fluid in outer chamber 98 is relieved and pressure is introduced to the advance fluid in advance chamber 70 from source line 161 (FIG. 2) through passage 160. Such an introduction of pressurized fluid into advance fluid chamber 70 causes piston vessel 63 to be displaced upwardly thereby causing expandable outer die section 1 to be displaced therewith upwardly around mandrel 59. Concurrently with the upward displacement of piston-vessel 63 and outer die section 110, additional forces are exerted against punch 109 through ram 139 to cause punch 109 to also be displaced upwardly. The upward displacement of expandable outer die section 1 10 and punch 135 is controlled so as to maintain the volume of die cavity 111 constant while varying its shape from that of billet 148 to that of a desired cup-shaped article 149 (FIG. 4). As discussed above, by maintaining the volume of die cavity 111 constant while varying its shape, the material of billet 148 can thereby be maintained both confined and pressurized so that the entire deformation process is accomplished with the material being maintained at the desired state of increased ductility.

The actual deformation of the billet 148 is accomplished by deforming forces cooperatively exerted by punch 109 and the threaded surface of forming die bore 129 on the billet material. The force exerted by punch 109 is a direct axial force generated through ram 139. The force exerted by the threaded surface of forming die bore 129, however, is a longitudinally exerted force which is transmitted to the billet material through the engagement of the billet material with the surfaces of thread 131. During the deformation, those portions of the billet material which are in the path of mandrel 59 as the billet is advanced thereover, are displaced laterally outwardly to form the wall portion of the cup-shaped article being formed. Once in the wall portion of the article, the billet material is advanced along the surface of mandrel 59 at the same velocity as outer die section 110 is being advanced and, in this manner, slippage between the surface of the material being deformed and the surface of die bore 124 is precluded.

In view of the different transverse cross-sectional areas of the billet 148 and the wall portion of article 149, and in view of the requirement of the process that the volume of the variable shape die cavity 111 be maintained constant once the billet is confined and pressurized, it can be seen that the speed of advance of expandable forming die 110 must be greater than the speed of advance of punch 135. Because of this relative speed of advance requirement, the complete elimination of relative movement between the billet material and the surface of forming die bore 129 is not possible. The present apparatus, however, is operated such that once the billet material passes the conical surface of the inner die section or mandrel 59 and becomes part of the wall of cup-shaped article 149, there is no relative movement between it and the surface of forming die bore 129. Thus friction losses between the outer surface of the billet material and the surface of expandable outer die section 110, are substantially eliminated.

Formation of cup-shaped article 149 from billet 148 is continued by the controlled advancement of punch 109 and expandable outer die section until the article 149 is completely formed as desired. At this point, the introduction of advance fluid into advance fluid chamber 70 is terminated, although the pressure in the fluid body is maintained, and the direction of movement of punch 109 is reversed by ram 139 to that punch 109 is withdrawn from forming die bore 129, punch bore 89 and ram bore 86, from the position of sown in FIG. 4 to that shown in FIG. 2.

AFter punch 109 has been withdrawn from the body of apparatus 40, the pressure of the advance fluid is relieved and pressure is reexerted on the retraction fluid in outer chamber 98 from retraction fluid source line (FIG. 2) through passage 154. The now pressurized retraction fluid causes the downward displacement of piston-vessel 63 from the position shown in FIG. 4 to that shown in FIG. 2. In that the pressure of the support fluid in support fluid chamber 1 17 has been maintained throughout the deformaton process, and since the outer surface of cup-shaped article 149 is in full engagement with the thread 131 of the forming die bore 129, downward displacement of expandable outer die section 110 with pistonvessel 63 causes the cup-shaped article 149 to be stripped from mandrel 59. When stripping is completed, the pressure of the support fluid in support fluid chamber 117 is relieved and the segments 112 of expandable outer die section 110 are caused to be displaced radially outwardly by the action of upper and lower spring elements 121, 122 against upper and lower die shoulders 118 and 119, respectively. The radially outward displacement of segments 112 by springs 121, 122 causes the threaded surface of forming die bore 129 to disengage the outer surface of cup-shaped article 149 thus permitting it to fall from the apparatus into a suitable bin. Although not necessary, the discharge of .the completely formed cup-shaped article is assisted by the introduction of a flow of ejection fluid, e.g. compressed air, into forming die bore 129 from source line 152, (FIG. 2) through passage 150, central chamber 97 and passages 101 in upper end cap 75.

With the finished article now discharged from the apparatus, a new blank 148 can be positioned within billet retainer cup 146 and the procedure can be repeated.

Cup-shaped article 149 is a finished article which requires no further manufacturing operations for completion. The segmented cylinder of outer die section 10 is prestressed by the pressure exerted by the support fluid in chamber 117 to a magnitude sufficient to preclude opening of the segments 112 during deformation, and article 149 is formed with substantially no flash. Further, the sliding movement of the billet material over mandrel 59 during deformation accomplishes a burnishing of the surface of the cup cavity which can obviate the necessity for any further surface finishing operations.

It may be desired to pass the finished article through a sizing die to eliminate the score marks caused by the thread 131 during deformation. This step is not ordinarily necessary, however, in that, as was discussed above, the depth of threads 131 can be made to be equal to or less than one half the diameter tolerance of the part being formed thereby ensuring that the formed part, with surface scores from thread 131, is still within tolerance for the finished article.

Thus, a complete process for manufacturing a cup-shaped article from bar stock and using the forming process of the present invention requires only the steps of cutting the bar stock to proper length, heat treating if it is desired to establish an initial ductility in the billet, and forming as described above. It may be desired to coat one end of the billet with a suitable lubricant, e.g. Indium or the like, to minimize friction between the billet material and the surface mandrel 59. Even with this additional step, however, the present process is simpler and less expensive than machining processes which heretofore have been required. In fact, savings in the range of an order of magnitude have been realized in the manufacture of cup-shaped articles according to the teaching of the present invention rather than by machining as in the prior art.

An additional advantage of the process of the present invention is that irregularly shaped articles can be formed which were not heretofore formable by drawing or extrusion and which, if manufactured by machining, would be so expensive as to render their manufacture commercially prohibitive. For example, an article having an elliptical outer cross section and a polygonal inner cross section could be manufactured by apparatus 40 merely by providing a polygonal mandrel 59 and by manufacturing forming die bore 129 of expandable die apparatus 110 to be elliptical rather than circular as shown. In all other regards the apparatus and process would be the same and an article, having been formed, would be ready for immediate use.

It will be understood that while the foregoing detailed description of the present invention has been taught in terms of forming solid plastic materials, the scope of the present invention also includes the forming of articles from materials or compositions, which may or may not fall within the above definition of solid plastic material, and which materials or compositions may be in the form of a slurry, or in granulated or comminuted form.

Finally, tubular articles having bores extending completely therethrough may be manufactured by the process and with.

the apparatus of the present invention by merely manufacturing a cup-shaped article in the manner described above and, thereafter, cutting off the base portion in any suitable manner. The advantages of manufacturing such tubular articles having through-bores in this way are that articles having varying inner and outer cross-sectional configurations can be manufactured from billets in a single forming operation coupled with a cutting operation, and the necessity for machining otherwise difficult to form tubular shapes is obviated.

It is to be understood that the above-described embodiments are merely illustrative of the principles of the method and of one embodiment of an apparatus according to the teaching of the present invention. Clearly, other embodiments thereof may be devised without departing from the scope of the invention.

What is claimed is:

1. Method of forming an article which comprises:

confining a quantity of material in a die system including an outer die, a punch, and a mandrel which together define an enclosed die cavity;

pressurizing said material by moving said die system; and

applying frictional force to the outer surface of said pressurized material by moving said outer die over said mandrel while maintaining said die cavity constant in volume and the material pressurized, to assist in forming said pressurized material over the end of said mandrel to produce said article.

2. Method of forming an article of solid plastic material, which comprises:

confining a blank of solid plastic material in a die system including an outer die, a punch, and a mandrel which together define an enclosed die cavity;

pressurizing said blank and increasing its ductility to a degree permitting deformation thereof without fracture by moving said die system; and

applying frictional force to the outer surface of said pressurized blank, by moving said outer die over said mandrel while maintaining said die cavity constant in volume and the blank pressurized to maintain said blank increasingly ductile, to assist in forming said increasingly ductile blank over the end of said mandrel to produce said article.

3. Method of forming an article form a billet of solid plastic material in a die having a variable shape die cavity, including the steps of:

a. positioning said billet of solid plastic material within said variable shape die cavity;

b. confining said billet within said variable shape die cavity,

the volume defined by said billet and said die cavity being equal;

c. pressurizing said confined billet to place said solid plastic material in a state of increased ductility;

d. applying frictional force to the outer surface of said confined billet of increasingly ductile solid plastic material to assist in forming said material over a forming member to form said article; and

e. maintaining the volume of said variable shape die cavity substantially constant during said step of material deformation to maintain said billet in said state of increased ductility.

4. Method of forming a cup-shaped article from a billet of solid plastic material in a die having an outer die section, a punch and a mandrel which cooperate to define a variable shape die cavity including the steps of:

a. positioning said billet of solid plastic material within said outer die section and between said punch and said mandrel;

b. confining said billet within said variable shape die cavity such as to place said billet in full surface-to-surface contact with the portions of said outer die section, said mandrel and said punch which define said variable shape die cavity, the volume of said billet and said die cavity being equal;

c. pressurizing said confined billet to place said solid plastic material in a state of increased ductility;

. exerting force against said punch to cause movement of said punch with respect to said mandrel and exerting a force against said outer die section to move said section over mandrel such as to vary the shape of said variable shape die cavity and shape said confined billet of increasingly ductile solid plastic material into said article; and

e. controlling the relative movement of said outer die section and said punch to maintain the volume of said variable shape die cavity substantially constant during the varying of the shape of said variable shape die cavity to maintain said billet in said state of increased ductility.

5. Method according to claim 4 wherein the inner surface of said outer die section is a high friction surface and wherein said step of compressing said confined billet includes the steps of exerting a force against said punch, and exerting a force against said outer die section, a longitudinal component of which force is transmitted to said solid plastic material through said high friction surface.

6. Apparatus for forming an article from a billet of solid plastic material, comprising:

a. outer die means;

b. punch means;

c. mandrel means;

d. said outer die means, said punch means and said mandrel means being relatively movable and cooperating to define a variable shape, enclosed die cavity; and

e. means for varying the relative positions of said punch means, and said mandrel means and for moving said outer die means over said mandrel to vary the shape of said enclosed die cavity so as to confine and pressurize said billet to increase the ductility of the solid plastic material thereof and to apply frictional force to the outer surface of said increasingly ductile material to assist in deforming said confined, pressurized billet over the end of said mandrel to form said article.

7. Apparatus as claimed in claim 6 wherein said outer die means comprises an outer die section having a die bore therein, and said die bore is provided with a high friction surface for frictionally engaging said outer surface of said material for applying said frictional force to the outer surface of said increasingly ductile material.

8. Apparatus as claimed in claim 7 wherein said outer die section comprises a plurality of generally wedge-shaped segments each having at least one arcuate surface thereon, said arcuate surfaces cooperating to define said die bore, and said segments being movable radially inwardly to apply said frictional force.

9. Apparatus as claimed in claim 7 wherein said high friction surface is defined by a thread formed in the surface of said die bore.

10. Apparatus as claimed in claim 6 wherein said means for varying the relative positions of said punch means, said mandrel means and said outer die means comprise means for reciprocably displacing said punch means and means for reciprocably displacing said outer die means.

1 1. Apparatus for forming a cup-shaped article from a billet of solid plastic material including:

a foundation member,

a machine block rigidly secured to said foundation member and having a main bore formed therein;

mandrel means rigidly secured within said machine block and having a portion extending into said main bore, said portion of said mandrel means extending into said main bore being configured in accordance with the desired configuration of the cavity of said cup-shaped article;

a piston-vessel mounted for reciprocating movement within said main bore of said machine block, said piston-vessel having a bore extending therethrough;

forming die means mounted in said piston-vessel for said die bore of said forming die means is a high friction surface.

13. Apparatus as claimed in claim 11 wherein said forming die means comprises an expandable forming die.

14. Apparatus as claimed in claim 13 wherein said expandable forming die is mounted within a chamber formed in said piston-vessel, said chamber for receiving pressurized fluid to provide radial support for said expandable forming die.

UNITED STATES PATENT OFT IQE cesrmmrs or eescri patent No. 31631306 l)atcd -jm"l1l 1*\ L. 19 7? inventor) John Ues-ley Archer and Francis Joseph Fuchs, Jr.

11 is certified that error appears in thc above-identified patent and that said Lcucrs Patent are hereby corrected as shown below:

In the specification; Column 1, line 21, delete line 22, before "solid." insert ----"----5 line &7, "come should read -some-; line 71, not" should read ---no--. Column 2, line 51, of f fracture" should. read 01 fracture- Column 3, line 37, "he" should read --the--=. Column 5, line after usulfimel inge'fll "'"-3 line 70 "of" second occurrenc' -fOI'--. Column 8, line 10, stopped" should I'CELU. stained-- 5 line 18, "relatively" should read --respective 'Ly line -13,

en should read --:.1nd--. Column 9, line 71, "plate" should read --plug Column 11, line 7, after the word "of" delete "cavity" Column 12, line 9, to" should read --so--5 line ll, "of sown should read --shown-; line 13, "AFter" should read ---Aitcr---. Column 13, line 21, solid plastic material, should read --"solid plastic material,

In the claims, Column 16, line 8, after "ant insert --said--.

Signed and sealed this 11 th day of July 1972.

( SEAL) Attest:

EDWARD ILFLETCHER, JR. I ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. Method of forming an article which comprises: confining a quantity of material in a die system including an outer die, a punch, and a mandrel which together define an enclosed die cavity; pressurizing said material by moving said die system; and applying frictional force to the outer surface of said pressurized material by moving said outer die over said mandrel while maintaining said die cavity constant in volume and the material pressurized, to assist in forming said pressurized material over the end of said mandrel to produce said article.
 2. Method of forming an article of solid plastic material, which comprises: confining a blank of solid plastic material in a die system including an outer die, a punch, and a mandrel which together define an enclosed die cavity; pressurizing said blank and increasing its ductility to a degree permitting deformation thereof without fracture by moving said die system; and applying frictional force to the outer surface of said pressurized blank, by moving said outer die over said mandrel while maintaining said die cavity constant in volume and the blank pressurized to maintain said blank increasingly ductile, to assist in forming said increasingly ductile bLank over the end of said mandrel to produce said article.
 3. Method of forming an article form a billet of solid plastic material in a die having a variable shape die cavity, including the steps of: a. positioning said billet of solid plastic material within said variable shape die cavity; b. confining said billet within said variable shape die cavity, the volume defined by said billet and said die cavity being equal; c. pressurizing said confined billet to place said solid plastic material in a state of increased ductility; d. applying frictional force to the outer surface of said confined billet of increasingly ductile solid plastic material to assist in forming said material over a forming member to form said article; and e. maintaining the volume of said variable shape die cavity substantially constant during said step of material deformation to maintain said billet in said state of increased ductility.
 4. Method of forming a cup-shaped article from a billet of solid plastic material in a die having an outer die section, a punch and a mandrel which cooperate to define a variable shape die cavity including the steps of: a. positioning said billet of solid plastic material within said outer die section and between said punch and said mandrel; b. confining said billet within said variable shape die cavity such as to place said billet in full surface-to-surface contact with the portions of said outer die section, said mandrel and said punch which define said variable shape die cavity, the volume of said billet and said die cavity being equal; c. pressurizing said confined billet to place said solid plastic material in a state of increased ductility; d. exerting a force against said punch to cause movement of said punch with respect to said mandrel and exerting a force against said outer die section to move said section over mandrel such as to vary the shape of said variable shape die cavity and shape said confined billet of increasingly ductile solid plastic material into said article; and e. controlling the relative movement of said outer die section and said punch to maintain the volume of said variable shape die cavity substantially constant during the varying of the shape of said variable shape die cavity to maintain said billet in said state of increased ductility.
 5. Method according to claim 4 wherein the inner surface of said outer die section is a high friction surface and wherein said step of compressing said confined billet includes the steps of exerting a force against said punch, and exerting a force against said outer die section, a longitudinal component of which force is transmitted to said solid plastic material through said high friction surface.
 6. Apparatus for forming an article from a billet of solid plastic material, comprising: a. outer die means; b. punch means; c. mandrel means; d. said outer die means, said punch means and said mandrel means being relatively movable and cooperating to define a variable shape, enclosed die cavity; and e. means for varying the relative positions of said punch means, and said mandrel means and for moving said outer die means over said mandrel to vary the shape of said enclosed die cavity so as to confine and pressurize said billet to increase the ductility of the solid plastic material thereof and to apply frictional force to the outer surface of said increasingly ductile material to assist in deforming said confined, pressurized billet over the end of said mandrel to form said article.
 7. Apparatus as claimed in claim 6 wherein said outer die means comprises an outer die section having a die bore therein, and said die bore is provided with a high friction surface for frictionally engaging said outer surface of said material for applying said frictional force to the outer surface of said increasingly ductile material.
 8. Apparatus as claimed in claim 7 wherein said outer die section comprises a plurality of geneRally wedge-shaped segments each having at least one arcuate surface thereon, said arcuate surfaces cooperating to define said die bore, and said segments being movable radially inwardly to apply said frictional force.
 9. Apparatus as claimed in claim 7 wherein said high friction surface is defined by a thread formed in the surface of said die bore.
 10. Apparatus as claimed in claim 6 wherein said means for varying the relative positions of said punch means, said mandrel means and said outer die means comprise means for reciprocably displacing said punch means and means for reciprocably displacing said outer die means.
 11. Apparatus for forming a cup-shaped article from a billet of solid plastic material including: a foundation member, a machine block rigidly secured to said foundation member and having a main bore formed therein; mandrel means rigidly secured within said machine block and having a portion extending into said main bore, said portion of said mandrel means extending into said main bore being configured in accordance with the desired configuration of the cavity of said cup-shaped article; a piston-vessel mounted for reciprocating movement within said main bore of said machine block, said piston-vessel having a bore extending therethrough; forming die means mounted in said piston-vessel for reciprocation therewith, said forming die means having a die bore formed therein into which said mandrel extends; punch means mounted for reciprocation into and out of said bore of said piston-vessel and said die bore of said forming die means; said mandrel means, said forming die means and said punch means cooperating to define an enclosed die cavity; and means for reciprocating said punch means and said forming die means to vary the shape of said enclosed die cavity.
 12. Apparatus as claimed in claim 11 wherein the surface of said die bore of said forming die means is a high friction surface.
 13. Apparatus as claimed in claim 11 wherein said forming die means comprises an expandable forming die.
 14. Apparatus as claimed in claim 13 wherein said expandable forming die is mounted within a chamber formed in said piston-vessel, said chamber for receiving pressurized fluid to provide radial support for said expandable forming die. 